Carbon grid for transmitting vacuum tubes



March 9 E. MOUROMTSEFF ET AL 2,193,600

CARBON GRID FOR TRANSMITTING VACUUM TUBES Filed April 10, 1935 2 Sheets-Sheet 1 INVENTORS S E S S vE N H W ATTORNE E. MOUROMTSEFF ET AL 2,193,600

CARBON GRID FOR TRANSMITTING VACUUM TUBES Filed April 10, 1935 2 Sheets-Shget 2 200 I fl/bEMo ATTORNE March 12, 1940.

WITNESSES:

Patented Mar. 12, 1940 PATENT OFFlCE CARBON GRID FOR TRANSMITTING I VACUUM TUBES Ilia E. Mouromtseff and Henry N. Kozanowski, Wilkinsburg, Pa., assignors to Westinghouse Electric & Manufacturing Company,

East

7 Pittsburgh, Pa., a corporation of Pennsylvania Application April 10, 1935, Serial No. 15,585 3 Claims. (01. 250-477 Our invention relates toelectron discharge devices and especially to such devices of the transmitting tube type in which a high voltage is placed upon the grid.

It is an object of our invention to prevent excessive secondary emission from the grid with increased plate voltage and thus prevent the grid current from rapidly decreasing in value and turning negative.

It is another object of our invention to substantially eliminate secondary electron emission from the-anode and to provide a more perfect heat absorbing surface on the interior thereof.

Other objects of our invention will become evident from the following detailed description taken in conjunction with the accompanying drawings in which:

Figure 1 is a partial view of an electron discharge device incorporating our invention and having a portion partially in section and the rest in side elevation.

Fig. 2 is a plan view of a carbon disc disclosed in Fig. 1.

Fig. 3 is .a plan view of a carbon spacer used in Fig. 1.

Fig. 4 is a graph disclosing the change in grid current with plate Voltage into tubes of the prior art; and

Fig. 5 is a graph disclosing the change in grid current with increased plate voltage in a tube incorporating our invention such as that disclosed in Fig. 1.

As stated above, it is an object of our invention to prevent excessive secondary emission from the grid and plate of power transmitting tubes. In its specific embodiment, we accomplish this result by forming our grid in these high power transmitting tubes of a structure that will withstand the high current andhigh voltage and yet one that will prevent any grid emission. In its specific embodiment, we utilize a plurality of annular carbon discs with carbon spacers therebetween for our grid structure.

The disclosure of our invention incorporated into a specific tube is in Fig. 1 in which reference character I is the insulating portion with the exterior anode l I preferably of copper sealed thereto at l2. The tube or container is formed with a reentrant portion l3 at one end thereof and through this reentrant portion is sealed two or more conductors l4 and I leading to the cathode structure. The cathode structure is preferably a plurality of strands IS in the form of tungsten filaments or ribbon extending longitudinally through the container and supported in position at the other end of the tubeby any suitable support H. The longitudinal portions of the filament are preferably parallel. Ad'- ditional supports It may also be located around the reentrant portion of the tube for the intervening portions of the filament It. It is preferable to have these cathode strands spaced concentrically in parallel arrangement about the axis of the tube. Around the cathode structure and preferably concentric therewith is the grid structure. form is a plurality of annular discs" or rings l9 such as is disclosed in both Figs.- 1 and 2. "In between these annular discs' or rings are carbon spacers 26 in the form of a small cylinder. The carbon rings l9 have a plurality of holes or'open-' ings 2i therethrough for the supporting rods 22. These rods are preferably equally spaced about the axis of the tube. The spacer has a central hole 23 to fit over one of these rods. A ring or clamp 24 preferably surrounds the reentrant portion l3 and has the upper portion of the rods 22 fastened thereto as by welding. The upper spacer 25 preferably bears against the reentrant portion at 28 to keep the carbon discs and spacers in position. Any suitable fastening means 21 such as a nut is on the lower end of the rods 22. These rods are preferably of some refractory metal such as tantalum or molybdenum. A conducting lead 28 is connected to the grid structure such as by welding to the metal band 24 and this rod is sealed through the glass or insulating portion of the tube at 29 to act as a lead for the grid.

It is preferred to have the cathode structure control electrode or grid structure and the anode concentric with the longitudinal axis of the operating portion of the tube.

When the tube is being evacuated, the grid is heated and a difference of potential placed upon the grid and anode. The anode is at a cooler temperature than the grid, with the result that tiny particles of carbon from the surface of the annular disc and cylindrical spacers are carried over to the anode andcoat the interior portion thereof with carbon.

In Figs. 4 and 5 are illustrated the diflerent results obtained with our structure over the devices of the prior art. In Fig. 4 is illustrated the values of grid current with increasing plate voltage in tubes of the prior art. The curve 30 illustrates the line where the plate voltage and the grid voltage are equal. As the plate voltage and its equivalent grid voltage are made greater, the grid current rises very rapidly. If, however, we

As previously stated, our preferred take the grid voltage and plate voltage at the value of 1400 volts and only increase the plate voltage, then the grid current will fall off very rapidly as illustrated by the curve 3| due to the redistribution of the plate and grid electrostatic fields whereby a greater portion of the emission current from the filament fiows to the plate. This current to the plate is also augmented by steadily increasing secondary emission from the grid. The grid-current decreases at other voltages as illustrated by curve 32 where the plate voltage is 600. If the plate voltage is increased, then the grid current will rapidly decrease to zero and even become negative. At the point 33 where this .curve passes the zero line, the grid begins to give oiT more electrons than it receives and thus produces the negative value of the grid current.

In Fig. 5 is disclosed a plurality of curves showing the prevention of secondary emission from the grid by use of our invention. In this figure, curve 4|] illustrates the grid current with equal plate voltage and grid voltage. The curve 4! discloses where the grid voltage is maintained at 1400 volts and the plate voltage steadily increased above that amount. The curve slopes ofi at first as the plate gets a greater portion of the cathode emission, but the curve slopes towards a parallel position with the zero line instead of sloping rapidly to it. The curve 42 for 600 volts on the grid discloses that the grid current decreases at first and then becomes a steady positive value with increasing plate voltage and does not cross the zero line. Accordingly in our structure with increase in plate voltage the plate absorbs a greater portion of the emission but the grid current does not become negative because secondary emission therefrom is substantially eliminated.

The carbon coating on the interior of the anode forms a more perfect heat absorbing surface thus assisting in the abstraction of heat from the interior of the tube. It is understood, of course, that any suitable cooling jacket is placed about the exterior anode II and a cooling medium such as a stream of water is passed rapidly over the exterior surface to remove excess heat therefrom.

Although we have shown and described certain specific embodiments of our invention, we are fully aware that many modifications thereof are possible. Our invention therefore, is not to be restricted except insofar as is necessitated by the prior art.

We claim as our invention:

1. An electron discharge device comprising a container having a tungsten cathode, a carbon control electrode and a copper anode, said anode being part of said container and having its interior wall coated with carbon.

2. A high vacuum tube comprising an anode forming a portion of the tube wall, a cathode of tungsten extending along the axis of the tube and a control-electrode between said cathode and anode, said control-electrode comprising coaxial carbon rings spaced apart from each other.

3. A high vacuum tube comprising a container wall having an anode portion and an insulating portion, said insulating portion having a press, a metallic band around said press, a plurality of metallic standards extending from said band, a tungsten cathode extending longitudinally of said container and a plurality of carbon rings and spacers on said metallic standards intermediate said tungsten filament and said anode.

ILIA E. MOUROMTSEFF. HENRY N. KOZANOWSKI. 

